Method of bending heat exchanger sections and a machine for the realization thereof

ABSTRACT

A method of bending heat exchanger sections and a machine for the realization thereof. The method consists in that the sections are compressed longitudinally to a critical state preceding the loss of stability by the tube material, after which the section is shaped in the desired direction.

United States Patent [191 Byzov et a1.

[ Aug. 27, 1974 METHOD OF BENDING HEAT EXCHANGER SECTIONS AND A MACHINE FOR THE REALIZATION THEREOF [56] References Cited UNITED STATES PATENTS 2,002,470 5/1935 Cornell 29/ 157 A 3,354,681 1l/1967 Lombard 29/157 A 3,597,956 8/1971 Clausing 72/305 3,667,274 6/1972 Cape 72/298 Primary Examiner-Charles W. Lanham Assistant Examiner-D. C. Crane [57] ABSTRACT [22] Flled' June 1971 A method of bending heat exchanger sections and a [21] Appl. No; 150,394 machine for the realization thereof. The method consists in that the sections are compressed longitudinally to a critical state preceding the loss of stability by the [52] US. Cl. 72/305, 29/2022lg,/Z59l5772./%8B9, tube material after which the Section is Shaped in the desired direction. [51] Int. Cl B2111 11/04 [58] Field of Search... 29/157.3 R, 202 D, 157.3 A, 3 Clailm, 3 Drawing Figures PATENTEB AUGZHQM MU 1 (I 3 FIG. 7

PATENIE AUG 2 7 I974 SHEET 3 0F 3 METHOD OF BENDING HEAT EXCHANGER SECTIONS AND A MACHINE FOR THE REALIZATION THEREOF The present invention relates to methods of bending and more specifically it relates to a method of bending heat exchanger sections and to a machine for the realization of the method.

The present invention will be used most successfully in the manufacture of heat exchangers whose sections have tubes with thin fins (0.25 to 0.5 mm) and which are intended for installation in cramped locations with convex-concave walls and small or round entrances, for example ships and automobiles.

Besides, the present invention will be useful for bending articles whose external surfaces are apt to be easily damaged.

Known in the art are a method of bending heat exchanger sections and a device for the realization thereof (Pat. No. 3.443.296, Cl.29 157.3, USA).

The known method provides for bending the sections consisting of two or more rows of tubes arranged in two or more parallel planes and passing through a multitude of flat parallel fins. Said method allows bending of sections only at an angle, for example at a right angle, which produces a box-shaped rectangular heat exchanger. This shape is not universally convenient for use in cramped locations mentioned above.

Besides, the products made by the known method call for additional treatment after bending, viz., expanding the tubes for ensuring the required contact between the tubes and the fins.

An object of the present invention resides in eliminating the aforesaid disadvantages.

The main object of the invention is to provide a method of bending heat exchanger sections, each section consisting of a row of tubes arranged in one plane and passing perpendicularly through a multitude of flat parallel fins, and a machine for the realization of said method, which can produce sections bent to two and more conjugate radii, which is necessary for making heat exchangers of a round shape or of a shape snugly fitting into the contour of a wall near which they are to be installed.

This object is accomplished by compressing the section tubes longitudinally to a critical state preceding the loss of buckling stability of the tube material after which a bending moment is applied to one end of the strained tube and the section is moved forward, thereby being bent and shaped in the desired direction.

Said method can be realized with the aid of a machine comprising a base with a device mounted on it for producing and maintaining the critical state in the material of the tubes at the moment of section bending, and for producing the bending moment for radiusbending of the sections, comprising an axle acted upon by a force which is required for producing the critical state preceding the loss of stability in the material of the section tubes. The machine has a bed on said base, one end of said bed carrying a master form set at a distance of the preset bending radius from the geometrical axis of said device, while its other end mounts a carriage for moving the sections along the master form. The carriage is provided with a drive and a built-in device for producing the bending moment for radiusbending, this device being coupled with the first one which clamps the tubes at one end of the sections, the

tubes at the other end being secured in the device for producing the bending moment in the course of bending the first radius.

To avoid damaging the tube fins while the section moves along the surface of the master form, the surface of the machine bed is covered with a metal strip, one end of which is secured to the axle of said device for maintaining the critical state of the tube material while its other end is secured on the carriage for moving the section along the master form.

Now the invention will be described in detail by way of example with reference to the accompanying drawings in which:

FIG. 1 is a general side view of the machine for bending the heat exchanger sections; 2

FIG. 2 is a section taken along line 11-11 in FIG. 1; and

FIG. 3 is a top plan view of the machine, partly in section, taken along line III-III in FIG. 1.

The machine for bending heat exchanger sections comprises a base 1 (FIG. 1) which mounts a device 2 for producing and maintaining the critical state of the tubes at the moment of section bending and for producing the bending moment when the section is. being bent to a radius R besides, the base supports a bed 3. Installed on one end of the bed 3 at a distance of the preset bending radius from the axle of said device 2-is a master form 4 which shapes the section. On the other end of the bed is installed a carriage 5 which moves the section along the master form 4. The carriage 5 is provided with a drive 6 which moves it along the master form 4 with a force greater than the oneproduced by said device 2 in order to allow movement of the section towards the master form 4, overcoming the'force procylinder 8 (see FIG. 3) and maintained within the limits insuring the critical state of the tube material in the process of bending.

The hydraulic cylinder 8 meshes with a gear wheel 10 via a gear rack 9 (FIGS. 2 and 3), said gear wheel 10 being mounted on one of the ends of the axle 7. The other end of said axle 7 carries levers l1 transmitting said force via a crosspiece 12 located on said levers 11 to the tubes of one end of the section, said tubes being located on said crosspiece. Besides, the levers 11 create, while turning around the axle 7, a bendingmoment applied to the tubes of this end of the section, these tubes being secured in the crosspiece 12.

FIG. 3 illustrates the connection between the hydraulic cylinder 8 and the wheel 10 by means of the rack 9. As the levers 11, coupled by way of a spline with the axle 7, turn as a result ofthe'movement of the carriage 5 and the master form 4, the wheel 10 coupled with the axle 7 moves the rack 9 which is at the end of the piston rod of the cylinder 8. The movement of the piston is impeded by the resistance of oil enclosed between the piston and the bottom of the hydraulic cylinder. Since oil is drained from the cavity of the latter through a pressure valve built in the hydraulic control system, the rotation of the levers I1 and the movement of the piston,

kinematically connected with the levers 11, help maintain a back pressure in the cylinder 8, its value depending on the adjustment of the spring of the pressure valve. The back pressure is maintained during firstradius bending.

Said carriage 5 has a built-in device 13 for producing a bending moment during bending to a radius R which is conjugate to the first radius R said device consisting of a drive 14 and a crosspiece 15 which is intended for fastening the tubes of the other end of the section and producing a bending radius during bending of tubes to a radius R which is conjugate to the first radius R one end of said crosspiece 15 is mounted in bearings 16 of the carriage 5 while its other end is coupled to its drive 14.

A socket in the crosspiece 15 accommodates a holder 17 with holes for fastening the ends of the tubes of the abovementioned end of the section.

FIGS. 1 through 3 show that the hydraulic cylinder 8 is connected with the carriage 5 kinematically through the following elements: (cylinder 8) rack 9, gear 10, axle 7, levers ll, crosspiece 12, section 4, holder 17, crosspiece 15 and bearings 16 (carriage 5). The cylinder does not differ much from other hydraulic cylinders in wide use, except that its rod ends with the rack 9. The carriage 5 has the two bearings 16, and the crosspiece (turnable frame) 15 has two half-axles entering into said bearings to connect the frame with the carriage. As shown in FlGS. 1 and 3, these bearings 16 are disposed on the carriage 5.

The tins of the section tubes are protected against damage in the course of their movement along a surface 18 of the master form 4, by placing a metal strip on a surface 19 of the machine bed 3. One end of the metal strip 20 is secured in a tensioning device 21 (FIG. 2) installed on the axle 7 between the levers 11 while its other end is fastened on said device 13 by means of spring compensators 22 located on the crosspiece 15. The spring compensators 22 make up for the difference between the developed length of the tube axis through which passes the neutral axis of section bending, and the developed length of the external surface of the section.

The metal strip is placed between the surface 19 and is adapted to pass freely under the turnable frame (crosspiece) 15, enveloping it from below, and it has one of its ends attached, as stated earlier, to the spring compensators 22 and, at the other end, to the strip tensioning device 21. To be bent, a section is placed on the metal strip 20 located between the surface 19 of the table 3 and the section with the holder 17 fixed in the crosspiece 15. The surface 19, or more accurately the plate of the table 3, has guides in which the carriage 5 slides with its tracks. The carriage, however, can only reciprocate along the table in the surface 19, while the crosspiece 15 turns about the carriage in its half-axles in the bearings 16, bending the pipes along the second radius. A cut 23, sufficient for the passage of the crosspiece 15, is provided in the surface 19 to allow the tuming of the crosspiece 15. The shaded region 24 on the top surface of the table in FIG. 3 shows schematically the section being bent.

The claimed machine operates as follows.

A heat exchanger section to be bent is fastened at one end by the ends of its tubes in the holes of the holder 17 while at the other end it is secured in the crosspiece 12.

Once the drive 6 has been switched on, the carriage 5 begins transmitting a force via the section tubes to the crosspiece 12 located on the levers 11.

In view of the fact that the levers secured on the axle 7 are connected by the gear wheel 10 and gear rack 9 with the constant-pressure hydraulic cylinder 8, the section tubes are compressed to a critical state preceding the loss of stability in the section tubes.

On reaching said critical state the carriage 5 starts moving towards the master form 4, overcoming the force applied by the cylinder 8 to the levers 11 and turning them around the axle 7.

Turning of the levers 11 around the axle 7 produces a bending moment on the ends of the section tubes secured in the holes of the crosspiece 12 installed on the levers 11; said bending moment bends the strained section to a radius R and forces it to take the shape of the surface 18 of the master form 4.

Turning, the levers 11 pull at an identical speed the metal strip 20 fastened to the tensioning device 21 and laid on the surface 19 of the machine bed 3 under the section, thus safeguarding the section fins against damage during their movement over the surface 18 of the master form 4.

Since the developed length of the neutral axis of bending coinciding with the axis of the section tubes is smaller than the developed length of the section external surface, the strip 20 remaining under the straight part of the section during bending, moves and compresses the springs of the compensators 22.

As soon as the preset length of the arc of the radius R, is obtained, the drive 6 is turned off and the carriage 5 stops.

For bending a section to the radius R which is conjugate with the radius R it is necessary to turn on the drive 14 of the device 13 built into the carriage 5; turning the crosspiece 15 with the holder 17, the drive produces a bending moment on the ends of the section tubes secured in the holes of the holder 17, said moment forcing the section to be bent to a radius R determined by the shape of the master form 4.

In the course of bending to a radius R the critical state in the material of the section tubes is maintained by the pressure of the hydraulic cylinder 8 transmitted via the levers 11.

The proposed method and machine allow the sections to be bent to two and more conjugate radiuses .and make it possible to manufacture compact but highly efficient heat exchangers from such sections, said heat exchangers having a round shape or a shape that fits easily into a space near the walls where they have to be installed.

The shape of such heat exchangers makes them suitable for use in cramped locations with curved walls.

Besides, bending of the sections by this method is carried out after final assembly and calls for no additional operations.

What is claimed is:

l. A method of bending a heat-exchanger section consisting of a row of section tubes lying in the same plane and passing perpendicularly through a plurality of flat parallel fins, comprising the steps of rigidly fastening the heat-exchanger section tubes to accomplish a bending process, applying an axial force to one end of the tubes, bringing the material of the tubes to a critical state, just preceding the loss of longitudinal stability, applying a lateral force to the other end of the tubes simultaneously with applying said forces to both ends of the tubes, and maintaining the critical state in the material all along the section tubes, without overstepping a predetermined critical point of the state in the material, and bending the section tubes to a preset radius.

2. A machine for bending a heat-exchanger section consisting of a row of section tubes lying in the same plane and passing perpendicularly through a plurality of flat parallel fins, themachine comprising, in combination, a base, a device for maintaining a critical state in the material of the section tubes during their bending and for producing a bending moment, said device including a single-arm lever to which one end of the section tubes is rigidly fixed, an axle mounted on said base, having one end to which said lever is fastened, a hydraulic cylinder wherein pressure is constantly maintained within required limits to maintain the critical state in the material of the tubes, a rack-and-pinion gear mounted at the other end of said axle and connecting the latter to said cylinder, a bed installed on said base, a master form for shaping the tubes, installed on one end of said bed, at a distance of a preset bending radius from said axle, a carriage for moving the tubes along said form and transmitting axial force to the ends thereof for producing the critical state in the material, just preceding the loss of longitudinal stability, mounted at the other end of said bed, a drive for said carriage for producing the axial force, a bending device for producing a bending moment during bending of the tubes to a preset radius which is conjugate with a first radius built into said carriage, a drive for said bending device which latter includes a turning crosspiece having two opposite ends, bearings by the aid of which said bending device is built into said carriage, one of said ends of the crosspiece being secured in said bearings, while the other end is connected to said drive and is adapted for fastening thereto the other ends of the section tubes.

3. The bending machine as defined in claim 2, further comprising a metal strip laid on the surface of said bed for protecting the fins of the section tubes against damage as the latter are moved along the surface of said form, one end of said strip being fastened to said axle of the maintaining device while the other end is secured to said bending device. 

1. A method of bending a heat-exchanger section consisting of a row of section tubes lying in the same plane and passing perpendicularly through a plurality of flat parallel fins, comprising the steps of rigidly fastening the heat-exchanger section tubes to accomplish a bending process, applying an axial force to one end of the tubes, bringing the material of the tubes to a critical state, just preceding the loss of longitudinal stability, applying a lateral force to the other end of the tubes simultaneously with applying said forces to both ends of the tubes, and maintaining the critical state in the material all along the section tubes, without overstepping a predetermined critical point of the state in the material, and bending the section tubes to a preset radius.
 2. A machine for bending a heat-exchanger section consisting of a row of section tubes lying in the same plane and passing perpendicularly through a plurality of flat parallel fins, the machine comprising, in combination, a base, a device for maintaining a critical state in the material of the section tubes during their bending and for producing a bending moment, said device including a single-arm lever to which one end of the section tubes is rigidly fixed, an axle mounted on said base, having one end to which said lever is fastened, a hydraulic cylinder wherein pressure is constantly maintained within required limits to maintain the critical state in the material of the tubes, a rack-and-pinion gear mounted at the other end of said axle and connecting the latter to said cylinder, a bed installed on said base, a master form for shaping the tubes, installed on one end of said bed, at a distance of a preset bending radius from said axle, a carriage for moving the tubes along said form and transmitting axial force to the ends thereof for producing the critical state in the material, just preceding the loss of longitudinal stability, moUnted at the other end of said bed, a drive for said carriage for producing the axial force, a bending device for producing a bending moment during bending of the tubes to a preset radius which is conjugate with a first radius built into said carriage, a drive for said bending device which latter includes a turning crosspiece having two opposite ends, bearings by the aid of which said bending device is built into said carriage, one of said ends of the crosspiece being secured in said bearings, while the other end is connected to said drive and is adapted for fastening thereto the other ends of the section tubes.
 3. The bending machine as defined in claim 2, further comprising a metal strip laid on the surface of said bed for protecting the fins of the section tubes against damage as the latter are moved along the surface of said form, one end of said strip being fastened to said axle of the maintaining device while the other end is secured to said bending device. 